One type of rotary fluid pressure devices is generally referred to as gerotors, gerotor type motors, and gerotor type pumps, hereinafter referred to as gerotor motors. Gerotor motors are compact in size, low in manufacturing cost, have a high-torque capacity ideally suited for such applications as turf equipment, agriculture and forestry machinery, mining and construction equipment, as well as winches, etc. Gerotor motors have gerotor sets, which utilize a special form of internal gear transmission consisting of two main elements: an inner rotor and an outer stator.
The inner rotor and the outer stator possess different centers. The inner rotor has a plurality of external teeth, which contact circular arcs on the interior of the outer stator when it revolves. Gerotor sets have volume chambers, which are separated by continuous contact between the rotor teeth and stator arcs. The volume changes as the rotor revolves with each chamber experiencing expansion or contraction. The rotary mechanism of the gerotor set, by virtue of its continuous chamber volume change, can be used as a positive displacement fluid controller. Gerotor motors, with a stationary outer stator and orbiting inner rotor, have a commutation device for valving flow to and from the chambers in time relation to the movement of the rotor. The output shaft is either directly connected to the orbiting inner rotor or is connected thereto by a drive link splined at each end. When pressurized fluid flows into a motor, the resistance of an external torsional load on the motor begins to build differential pressure, which in turn causes the inner rotor to rotate in the desired direction via a timing valve.
Gerotor motors are typically manufactured in two forms, an internally generated rotor (hereinafter referred to as “IGR”) gerotor set or an externally generated rotor (hereinafter referred to as “EGR”) gerotor set. The outer stator of both IGR and EGR gerotor sets have one more tooth (N+1 teeth) than the inner rotor (N teeth). When the inner rotor rotates, it also orbits in the opposite direction of rotation with the speed of N times its own rotation. The vane pocket of the EGR is located on the outer stator and the vane pocket of the IGR is located on the inner rotor. During the motor operation, roller vanes mesh with external gear teeth of the inner rotor for an EGR rotor set and mesh with internal gear teeth of the outer ring for an IGR rotor set.
For both EGR and IGR gerotor sets, the inner rotor can be used as a timing device for valving fluid in a timely manner. Prior art, such as U.S. Pat. No. 2,989,952 to Charlson, and U.S. Pat. No. 3,825,376 to Peterson et al., use EGR gerotor sets which do not efficiently use the inner rotor as a timing device due to the number of volume chambers being one larger than the number of external teeth, and thus one larger than the fluid passages in the inner rotor. This extra volume chamber is trapped during operation, creating excessive high pressure or cavitation during operation. To avoid this, the working fluid has to be detoured into each fluid chamber via a side manifold plate and cannot be directly valved within the EGR gerotor set. The present invention is able to use flow passages in the inner rotor for direct valving since the number of fluid chambers and number of flow passages are the same. The previously-noted prior art patents also use the bearing surface of the inner rotor for openings of the passages into the volume chambers which causes stress concentration and significantly reduces the life of the gerotor set. The U.S. Pat. No. 3,825,376 also has the passageway opening at the bottom-most point of the rotor external gear. Typically, the peaks and valleys of the bearing surfaces are used for sealing. Placing an opening at the valley allows for cross-port leakage which in turn causes poor volumetric efficiency.
Prior art designs use conventional wear plate assemblies and conventional disk valve assemblies, which typically consist of a rotary disk valve driven by a drive link, a stationary manifold, and a pressure compensation device to close off the clearance of the valve interface at high pressure. The present invention eliminates the wear plate, since the manifold serves as a wear plate between the front housing and the gerotor set, and eliminates the disk valve assembly, since the valving function has been integrated into the rotor. The elimination of these components significantly reduces the number of parts for the gerotor motor. Consequently it reduces the number of areas where cross-port leakage can occur.
In other prior art constructions, such as those set forth in U.S. Pat. Nos. 4,357,133, 4,697,997, 4,717,320 and 4,872,819 all to White, Jr., the motor uses a conventional EGR gerotor set. A circular commutator ring is integrated on the rotor for fast speed valving of the motor. To avoid possible high no-load pressure drops caused by narrow fluid passages and to reduce the length of the motor, these motors use an inner rotor with a very aggressive rotor profile, having a large eccentricity. Therefore, the drive link of the motor has a very large wobble angle. This causes heavy contact stress on the splines of the drive link, which may reduce the torque capacity or life of the drive link. In order to reduce the large wobble angle of the drive link, these motors are extended by making the drive link longer. The present invention has a similar volume displacement capability of these prior art EGR gerotor motors while having half the eccentricity. This 50% reduction of eccentricity significantly reduces the wobble angle of the drive line. Therefore, the splines of each end of the drive link in the present invention need not be heavily crowned. Also, the contact area of the external (drive link) and internal (rotor and drive shaft) splines is larger than those of the prior art. This increase in spline contact area improves the torque capacity of the drive link and makes the motor more reliable when operated under a high torque load.
In another prior art reference, U.S. Pat. No. 4,741,681 to Bernstrom, the rotary fluid pressure device utilizes a valve-in-star (rotor) type valving. This prior art structure is different from the present invention in several areas. First, the valve-in-star uses an EGR gerotor set rather than the IGR gerotor set, as is the case in the present invention. It is also limited to closed-loop applications due to its intrinsic imbalance, having three pressures at the front side of the rotor and two pressures at the rear side of the rotor. This prior art structure also uses a side plate/manifold to reach the gerotor set volume chambers. Specifically, pressurized fluid flows through the manifold, to the rotor, back to the manifold after timely valving, and then reaches the volume chambers. As noted above, the present invention uses its rotor for direct fluid valving.